The aspartyl residues in metabolically stable proteins have been found to undergo racemization in long-lived mammals. This racemization forms the basis of a biochronological tool useful for assessing the ages of mammals, including humans. Racemization may also cause changes in the functionality of metabolically stable proteins and thus be part of the aging process in long-lived mammals. The objectives of the research proposed here are to more conclusively ascertain the possible role of racemization in aging and/or protein turnover, and to further refine the biochronological application of racemization. Specifically, we propose to determine whether neighboring amino acid residues have any effect on racemization rates. So far as we have determined the extent of racemization of the total aspartic acid residues in several different model proteins. However, there may be a large variability of racemization rates for the various aspartyl residues. To test this we will carry out some sequencing experiments on proteins obtained from the lens nucleus and determine the extent of racemization of individual residues in these proteins. We also propose to continue our work on the use of aspartic acid racemization in teeth and the lens nucleus as an indication of the age of various mammals. We have arranged to obtain teeth and lens samples from individuals living in Georgian Russia who claim exceptional longevity. The analyses of these samples and the confirmation that the individuals are indeed as old as they claim would be of fundamental importance to gerontological research.